<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="./vue.js"></script>
</head>
<body>
<div id="app">
    <div contenteditable="true" v-on:input="inputHandler" v-once="">
        {{ content }}
    </div>
    <br>
    <div>{{ content }}</div>
</div>

<script>
    let app = new Vue({
        el: '#app',
        data: {
            content: 'Div content editable.',
        },
        methods: {
            inputHandler(event_) {
                this.content = event_.currentTarget.innerText;
                console.log(this.content);
            },
        }
    });
</script>
</body>
</html>